Background
In explaining the reason for their study, the authors write that "sea level change is an important scientific topic, particularly as there is concern about rising sea levels and the significant impact this could have on growing coastal communities (Nicholls and Cazenave, 2010)," while they say that their focus on the North Sea was the result of the fact that it "is one of the most densely populated coastlines in the world with a coastal flood plain population of roughly 15 million people."

What was learned
The nine researchers - hailing from Australia, France, Germany, the Netherlands and the United Kingdom - determined that (1) the long-term absolute mean sea level trend for the entire North Sea between 1900 and 2011 was 1.53 ± 0.16 mm/yr, that (2) for the English Channel the corresponding rate was 1.18 ± 0.16 mm/yr, which they say was consistent with the findings of Woodworth et al. (2009), who estimated the geocentric component of sea level rise to be 1.4 ± 0.2 mm/yr, based on what they say were "a few long UK tide gauge records," that (3) "recent rates of sea level rise are considerably higher, with the highest rates at the end of the 20th century," although they indicate they are still of the same order of magnitude as "those which have been observed at earlier times in the 19th and 20th century," and that (4) "long-term sea level trends in the North Sea are similar to global long-term sea level trends, but are higher for the last few decades compared to the global mean," although they say that the "differences between regional and global sea level rise are not yet statistically significant."

What it means
In light of the findings of the international team of scientists participating in this significant study, it would appear that there is nothing unusual, unnatural or unprecedented about the rate of sea level rise throughout both the North Sea and the rest of the Global Ocean over the entire CO2-emitting course of the Industrial Revolution.